Atherosclerotic disease is a leading cause of death in the industrialized world, particularly in the United States. Many heart attacks and strokes are caused in part by a narrowed, stenosed blood vessel. A medical procedure commonly used to deal with vessel stenosis is angioplasty. Angioplasty, in particular Percutaneous Transluminal Angioplasty (PTA), includes inserting a balloon catheter into the femoral artery near the groin, and advancing the catheter to the stenosis. The balloon can then be inflated to widen or dilate the narrowed region. The balloon catheter can then be withdrawn. In some cases, the widened vessel rebounds or re-closes, narrowing the vessel over a period of time.
Stents have come into increasing use to prevent the widened vessel regions from narrowing after angioplasty. A stent, typically having a tubular shape, can be put in place in the widened vessel region to hold the vessel walls apart and the lumen open in the event the conditions would otherwise result in re-stenosis. One class of stents requires that the stent be forcibly outwardly expanded to put the stent into position against the vessel walls. Another class of stents, self-expanding stents, can be delivered to a site in a compressed or constrained configuration and released in the vessel region to be supported. The self-expanding stent then expands in place to a configuration having a wide lumen, typically pressing firmly against the vessel walls where released. The stent is commonly placed at a recently dilated, stenosed vessel region.
Self-expanding stents can be delivered to a target site mounted over an inner tube or shaft and constrained within the distal end of an enclosing retractable tube or sleeve. The self-expanding stent can be freed from the restraint of the outer sheath by either distally pushing the inner shaft against the stent or proximally pulling the retractable outer sheath from over the stent. Once free of the outer restraint, the self-expanding stent can expand to force itself against the vessel inner walls. Self-expanding stents are often elastically biased to assume an original larger shape after being temporarily compressed into a smaller size to more easily be transported through blood vessels to the target site. There is an ongoing need for improvements in catheters that deliver self-expanding stents.